<!DOCTYPE HTML>
<html>
<head>
	<script type="text/javascript">
		function getIndex(){
			var x=document.getElementById("mySelect")
			alert(x.selectedIndex)
			x.selectedIndex = 0;
		}
	</script>
</head>
<body>

	<form>
		Select your favorite fruit:
		<select id="mySelect">
		  <option>Apple</option>
		  <option>Orange</option>
		  <option>Pineapple</option>
		  <option>Banana</option>
		</select>
		<br /><br />
		<input type="button" onclick="getIndex()" value="Alert index of selected option"/>
	</form>

</body>
</html>